Phred said -> [Light causes the ground to heat up. (light becomes heat) ]
Actually, light has potential energy and when it strikes the earth, this potential energy is changed into kinetic energy. This is like a car going 90 mph, hitting a concrete barrier. The car isn't converted into energy but the potential energy of the car's velocity and mass ... is converted into kinetic energy.
Phred-> [The ground radiates that heat into the atmosphere.]
Yes. It does so by emitting light in the spectrum of infrared ... which we can't see with our eyes but can feel on our skin. This is the type of heat we feel when we walk close to a large rock exposed to direct sunlight. Even though we don't touch the rock with our body ... we can feel it "radiating" heat.
Phred->[The more Co2 there is in the atmosphere the more heat it will trap within.
CO2 doesn't trap any heat; it ABSORBS heat. Just like a frying pan on a burner ... the pan will seemingly stop the radiated heat from the burner -for a time- while it is absorbing heat ... but then the pan gets hot and radiates heat just like the burner did before the pan was put on top of it. CO2 works exactly the same way. Where our own atmospheric gases of Nitrogen and oxygen DON'T absorb infrared radiation coming off the ground -(they let it pass through untouched) ... CO2 does ... and it warms up ... and then it radiates the heat it absorbs, just like a frying pan on a burner.
Phred->[Venus wasn't always an atmosphere of sulphuric acid. Light still penetrates it even though the clouds completely cover it. And now it doesn't take much to heat it up.]
Very little light gets down to the surface of Venus; it's really dark on the surface. Most of the sun's light is reflected off the sulfurous clouds surrounding the planet's upper atmosphere -- which is why we can see Venus in the sky as a very bright "star". And so ... it doesn't receive much heat from the sun at all. I don't know why you say that "it doesn't take much to heat it up" because the planet is shielded from the sun by a reflective cover ... and then a heavy insulation blanket underneath that.
If you put a reflective coating -like tinfoil- over a blanket of insulation ... you can stand behind that barrier in front of a raging fire ... and get no heat from the fire on your skin. That's Venus for you. So where DOES it get all of its heat FROM? It's hotter than Mercury and Mercury is closer to the sun. How can that be ... unless there's a heating source INSIDE of the planet of Venus?
Furthermore, the sun only strikes Venus on a single side at any given time. On the other hand, Venus is radiating as much heat outward as can manage to penetrate inward. Insulation and reflection work exactly the same in both directions. BUT .... Venus radiates whatever limited amount can get through its barriers ... IN ALL DIRECTIONS
... whereas the sun's rays are only striking it on one side. The net effect of that is that Venus should be cooling down faster than it can be warming up from the sun's rays.